Coated lamp bulb



Nov..3, 1931. s, us j 1,830,165

COATED LAMP BULB Filed Dec. 10. 1927 INVENTOR D. ,5. G05 Tl/V ATTORNEY L0 luoent hollow body Patented Nov. 3, 1931 DANIEL B. GUSTIN,

GQHI'LNY, A CORPORATION OF PENNSYLVANIA COATED LAMP BULB Application Med December 10, 1927. Serial in. 239,244.

This invention relates to the process of coating or to the ap lication of a painter the like to an incan escent lamp bulb and relates more particularl to the coating of a 5 bulb on the interior wall thereof such as disclosed in copending aplication of Aaron M. Hageman and Albert F. Lindstrom, Serial No. 238,734 filed December 9, 1927 for method and apparatus for coating the interior 0 wall "of hollow bodies and assigned to the same assignee as is the present invention.

As set forth in the above mentiohed copending application, lamps are sprayed with a finely divlded material, preferably a com 5 position including a igment, a filler and a sodium silicate bin er. This preparation when sprayed upon the inner wall of the bulb produces a light difiusing medium which in addition to the glossy outer surface of the 0 bulb results in a pearly or opalescent effect.

The present invention aims to improve the light diffusing characteristics of a lamp coating as above mentioned and provides or the additional application of a film or layer of transparent or translucent substance which will improve the light transmitting properties of the layer.

The present method consists in spraying the inner surface of a bulb or other transwith a pigment mixed with a small quantlty of sodium silicate as a binder. The coated article is then subjected to a baking treatment so as to dehydrate the coating and set the same. After this initial 5 coating has been properly set, it is again sprayed with a light difiusing coating such as kaolin to which has been added a relatively large amount of sodium silicate as a binder. This double coating of the lamp gives the same a pleasing appearance and eliminate any glare that may result as when a high temperature concentrated filamentary light source is employed.

interior wall of a lamp bulb with a composition including sodium silicate that the sodium silicate acts to set upstrains upon the surface of the bulb to such a degree that if any appreciable amount of sodium silicate is employed the bulb becomes brittle and It has been found that when coating the cracks upon a relatively small degree of impact as may be caused by handling or general transportation. It 1s, therefore, necesa sodium silicate binder having a specific gravity of about 1.05. This makes it 0ssible to produce an inside coated lamp aving such an amount of sodium silicate as to give the desired light" diffusion to the same degree as is possible with bulbs having the,

coating upon the outer surface thereof in which the'sodium silicate content is relatively large, inasmuch as the use of sodium silicate on the outside of the bulb has a tendency to strengthen rather than weaken the bulb.

It has further been found that upon coating lamp bulbs upon the inside surface thereof, certain of such lamps when in use tend to blacken, as for example, a lamp coating containing sienna and sodium silicate. This blackening may be due to the use of phosphorous which is employed as a getter in the lamp during the exhausting operation, the phosphorous reacting with the coating and reducing it, thus causing a blackening of the bulb. i

. Tests have been made using alight difiusing coating containing sodium silicate which is baked on the bulb, the coating composition 01' BLOOMI'IELD, NEW JERSEY, ASSIGNOB TO WEBTINGKOUBEJW containing, for example, sienna as a pigment I mixed with silicate. After thiscoating has been baked, it was given a layer of sodium silicate. Other lamps were sprayed with sienna, kaolin and sodium silicate and also given an additional layer of sodium -silicate. It was found that when given the subsequent sodium silicate layer the lamps did not blacken or become gassy and it seems that by coating the first sprayed layer with sodium silicate the said layer is prevented from reacting with the getter as, for example, in the case of sienna and kaolin, forming a more stable compound which does not evolve moisture. 'The general effect of the addition of sodium silicate to the interior of the bulb is to promote the vacuum and improve the quality of the lamp. This being true whether the sodium silicate is deposited on the coating or on other. portions of the internal structure of the bulb as, for example, a deposit of sodium silicate on the stem will give advantageous results.

n example of a coating composition which may be. used as an initial coating may contain a filler, coloring pigment and other materials as to provide a translucent surface when applied to a bulb. The coating may be prepared by mixing 250 grams of finely divided kaolin with 1000 cc. of a solution of sodium silicate having a specificgravity of about 1.025; -or a coating may bejprepared by mixing 125 grams of kaolin with 700 cc. of a solution of sodium silicate having a specific gravity of about 1.025. The kaolin may be substituted for a color pigment or the pigment may be added to the mixture which includes kaolin. It is to be understood that such quantity of pigment may be used as to give the proper depth of color to the composition. The mixture may then be placed in a ball mill mixer and milled for a suitable period as, for example, about 15 hours. The coating material may be applied by pouring into a bulb or preferably by spraying as shown and described in the above mentioned copending application.

The bulb or the like, after the application of the coating preparation, is subjected to a relatively high degree of heat for a predetermined period of time in order that the preparation may become properly fixed to the bulb surface. It has been found that by placing the bulb in an oven heated to about 150 C.

and allowing it to refain there for about 2 minutes the preparation becomes firmly fixed in a satisfactory manner. After the bulb has been heated and the coating has set, a second layer ofs odium silicate of about 1.05 specific gravity may be applied to the initial coating. This latter layer is preferably applied while the bulb is still heated, although the same may be deposited upon the initial coat after the same has cooled.

It will be understood that the exact proportions of the ingredients depends upon the light diffusing requirements of the coating and upon the color and density desired, it being understood that the foregoing example is given as one practical embodiment of the invention.

A bulb coated in accordance with the present invention is shown in the single figure of the accompanying drawing. As illustrated a bulb 2 may be provided with a layer 3 of light diffusing material, which layer may be encased in another layer 4.- of sodium silicate as above set forth. It is obvious that although the coating as shown is applied to the interior surface of the bulb, it may be applied to either the inner'or the outer surface.

Although the use of a supplemental layer of sodium silicate is advantageous in enhancing the apearance of the initial coating of the bulb, it will be'evident that it'serves a double function in that it acts as a clean-up agent.

After a lamp bulb has been coated, it is necessary to "seal the same to a lamp mount 1 which supports the internal structure of the bulb. After the mount has been scaled 'into the bulb, the exhaust tube of the bulb is applied to an exhaustmachine. The exhausting method includes the heating of the bulb and i as an explanation of the action of the sodium silicate, it may be stated that the silicate is dehydrated when the bulb is heated up during exhaust and that when it cools down it has a high aflinity for moisture. This func- E tion of the sodium silicate is important since it will reduce the tendency toward loss of vacuum in lamps, also brittle filaments and black lamps or gassy lamps.

It has been found that good results are ob- 9 tained when the internal structure of the device includes an element containing a sodium silicate as, for example, a lamp having a zirconium button which contains sodium silicate as a binder, has been found to 9 have a getter effect to hold orimprove the vacuum within a sealed envelope. The dual function of the sodium silicate within an electrical device such, for example, as an in-.

teriorly coated incandescent electric lamp is It to enhance the appearance of the coating and to permit the operativeness of the device.

As above set forth, the coating material may be what is termed a wet coating and applied by flushing or spraying. It is to be understood, however, that a so-called dry initial coating may be used; that is, the initial coating material may be in powdered form and dusted onto the interior surface of the bulb after which the sodium silicate layer may be applied. Dry coatings do not employ any binder such as sodium silicate so that when given an additional coating of sodium silicate in accordance with the present invention, a more lustrous appearance is given to the bulb. It has been the practice when dry coating bulbs to first etch the interior surface thereof and it has been found that a bulb etched and dry coated with an additional layer of sodium solicate gives a pleasing result.

Although a preferred embodiment of the invention is shown and described herein, it

is to be understood that modifications may be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. A lamp bulb having a light diffusing lit coating on a surface thereof and a .layer of sodium silicate enclosing said coating. 2. A lamp bulb comprising a light difiusing coating including a filler, a sodium sili- I cute and a sodium silicate layer enclosing said coating. In testimony whereof, I have hereunto subscribed my name this 8th day of December DANIEL S. GUSTIN 

